In modern terms, vigilantes are secret militias or police which attempt law enforcement, in the usual phrase, "by taking the law into their own hands".

In the United States vigilantism was especially strong in Montana during the days of the gold rush and in California during the struggle for control of the gold fields after the gold rush of 1849 and during labor unrest between the World Wars. However vigilantism frequently broke out in other areas of the country and often resulted in lynching of suspected criminals.

In Spanish, vigilante means 'watchman', which is how many of these groups started, where there was no organized law enforcement.